Inclusive Dijet Production at Low Bjorken-x in Deep Inelastic Scattering
H1 Collaboration
TL;DR
This study measures inclusive dijet production in DIS at low $x$ and low-to-moderate $Q^2$ with the H1 detector, comparing multi-differential cross sections to NLO DGLAP QCD and to non-DGLAP models (CCFM/CASCADE, ARIADNE, RAPGAP with virtual-photon structure). While NLO DGLAP adequately describes the dijet cross sections, the azimuthal separation observable S reveals enhanced non-$k_t$-ordered emissions at low $x$ and $Q^2$, challenging pure DGLAP dynamics. Models incorporating unintegrated gluon densities (CASCADE) and color-dipole cascades (ARIADNE) describe S better in certain regions, enabling constraints on the underlying low-$x$ gluon structure. The results thus advance understanding of parton cascades in DIS and provide valuable input for modeling unintegrated gluon distributions relevant to QCD at small $x$.
Abstract
Dijet production in deep inelastic ep scattering is investigated in the region of low values of the Bjorken-variable x (10^-4 < x < 10^-2) and low photon virtualities Q^2 (5 < Q^2 < 100 GeV^2). The measured dijet cross sections are compared with perturbative QCD calculations in next-to-leading order. For most dijet variables studied, these calculations can provide a reasonable description of the data over the full phase space region covered, including the region of very low x. However, large discrepancies are observed for events with small separation in azimuth between the two highest transverse momentum jets. This region of phase space is described better by predictions based on the CCFM evolution equation, which incorporates k_t factorized unintegrated parton distributions. A reasonable description is also obtained using the Color Dipole Model or models incorporating virtual photon structure.